A Western Australian Nationals' MP wants an inquiry into the scheme which subsidises medical travel for regional residents, saying part of its requirements are "antiquated" and cause major difficulties.

The Pastoralists and Graziers Association (PGA) says a voluntary code of conduct between major supermarkets and food manufacturers is a step in the right direction but it has doubts about how effective it will be.

The Pastoralists and Graziers Association (PGA) of Western Australia says the protracted debate over the potential sale of a major eastern states grain handler to an American company is sending a "terrible message" to foreign investors.